Quite unusual you get sourness all the time. Some blends i've tried have zero sourness. Some is all about fruits and acidity (aka "sourness").
1st do a check of your thermostat to see if its in the correct range and not malfuctioning. Heat machine for 20 mins. When the boiler light immediately goes off, press brew button. Is there super heated water (steam + bubbly water + hissing) coming out of the shower screen? If yes then the thermostat should be within the range and able to heat your water enough.
2nd - Use a medium/ darker roasted blend. Highlander. Papa's nut and boltz, are ok. for even darker traditional stuff try toby's, oriole, or coffee in a place stuff (red bird, perfero, bodka - all are sublime).
Avoid nylon, strangers reunion. Excellent coffee but usually light roasted and not easy to pull a good shot.
3rd - Don't use a flushing technique to get your water to the correct temperature. The flushing technique is quick and dirty way to get temp to ideal but not easy to use may drop boiler pressure too much. Use a temp surf technique.
1. 20 mins to warm up machine (with portafilter inside)
2. When the boiler light goes off, you may start to prep your filter basket. Exactly 2 mins after boiler light goes off, press the brew button and extract the coffee.
If still too sour decrease the waiting time - eg 1min 30 secs, 1 min
If bitter then increase the waiting time. - eg 2 min 30 secs. etc.
4th - Use dose that is appropriate for the basket. Using stock double basket? Keep it to 14-15g. Better still. use stock baskets and keep dose to 15g. (i usually don't advocate extremely low doses although it might solve sourness problems cos i find too much headspace between the top of the puck and shower screen causes channeling).
5th - Keep extraction time between 25-30 secs. Better still. keep extraction time to exactly 30 secs since you are trouble shooting.
6th - keep your brew ratio to 2. 15g dose = 30g of espresso cos you are troubleshooting. Let grind size control flow rate to get 30g of espresso in 30 secs with 15g of coffee.
lastly - try to ensure you don't have an uneven extraction. use a bottomless portafilter. (uneven extraction causes extreme bitterness rather than sourness actually but good practice for consistency to use bottomlesss portafilter).
In general, sourness can be due to:
a. inherent bean characteristic (natural processed, varietal etc).
b. light roast (vegetal kind of acidity may be due to underdeveloped roast).
c. under extraction (AKA low extraction yield - too high dose, too short brew time, too low brew ratio, low brewing temps)
Contrary to visual judgement a very dark sinister slow flowing shot (eg 45sec extraction with very low brew ratio of 1:1) is usuallyU]under[/U] extracted not over extracted. Flavours may be very intense and bitterness is always picked up first because of the way we perceive different flavours when they are in higher concentration. Sourness is still there actually.
Good luck in your experiments!
